Asus Z9PE-D16-10G/DUAL - Manual (Page 44)

2-24 Chapter 2: Hardware information
8. Q-Code LEDs
The Q-Code LED provides you a 2-digit display that shows the system status. Refer to
the Q-Code table below for more details.
7. CATT LED
The CATT LED indicates that the system has experienced a fatal or catastrophic error
and cannot continue to operate.